Prior studies suggest that intestinal disease, primarily proctitis and proctocolitis, is a frequent problem in homosexual men. A variety of pathogens have been implicated including commonly-recognized transmissible agents of enteric disease as well as multiple organisms recognized as agents of sexually transmitted diseases. More recent work also indicates that diarrhea and opportunistic infection are common features of AIDS and the AIDS-related complex. The purpose of our study will be to examine enteric pathogens and enteric disease in homosexual men, a group at risk for AIDS. The source of participants will be another study entitled "Natural History of AIDS in Homosexual Men". This parent study involves a cohort of 1,000 homosexual men from the Greater Baltimore area who are followed a six month intervals for three years with the major goal of identifying variables associated with altered immune status and the risk of developing immune defects including AIDS. Our studies will include analyses of rectal swabs or stools to detect 20 infectious agents including N. gonorrhoeae, T. pallidum, C. trachomatis (including LGV strains), H. simplex, CMV, Giardia, E. histolytica, Cryptosporidium, Isospora, Salmonella, Shigella, Campylobacter, Aeromonas, C. difficile, Yersinia, Vibrio, rotavirus, adenovirus, Coxsackie viruses and C. albicans. There will be three studies: 1) a prevalence study involving cross-sectional analysis from a randomly selected population of 200 patients; 2) a case-control study to define the incidence, clinical characteristics and agents of symptomatic disease among the 1,000 participants followed prospectively for 3 years; 3) an epidemiologic study designed to detect carriage of pathogens in sexual contacts of patients with symptomatic disease; and 4) an intensive evaluation of intestinal disease in participants and patients that develop AIDS for AIDS-related complex. A unique aspect of this work is that extensive data will be obtained in the parent study to define behavioral practices and to define immune function of participants. This information, which does not require separate funding, will be included in data analysis of the present study to identify risk factors associated with intestinal carriage or symptomatic disease and to examine possible relationships between enteric infections and alterations in the immune system.